The MAP_PROJ_INIT function initializes a mapping projection, using either IDL's own map projections or map projections from the U.S. Geological Survey's General Cartographic Transformation Package (GCTP). GCTP version 2.0 is included with IDL.
| Note |
This routine is written in the IDL language. Its source code can be found in map_proj_init.pro in the lib subdirectory of the IDL distribution.
Result = MAP_PROJ_INIT(Projection [, DATUM=value] [, /GCTP] [, LIMIT=vector] [, /RADIANS] [, /RELAXED] )
Keywords-Projection Parameters:
[, CENTER_AZIMUTH=value] [, CENTER_LATITUDE=value] [, CENTER_LONGITUDE=value] [, FALSE_EASTING=value] [, FALSE_NORTHING=value] [, HEIGHT=value] [, HOM_AZIM_LONGITUDE=value] [, HOM_AZIM_ANGLE=value] [, HOM_LATITUDE1=value] [, HOM_LATITUDE2=value] [, HOM_LONGITUDE1=value] [, HOM_LONGITUDE2=value] [, IS_ZONES=value] [, IS_JUSTIFY=value] [, MERCATOR_SCALE=value] [, OEA_ANGLE=value] [, OEA_SHAPEM=value] [, OEA_SHAPEN=value] [, ROTATION=value] [, SEMIMAJOR_AXIS=value] [, SEMIMINOR_AXIS=value] [, SOM_INCLINATION=value] [, SOM_LONGITUDE=value] [, SOM_PERIOD=value] [, SOM_RATIO=value] [, SOM_FLAG=value] [, SOM_LANDSAT_NUMBER=value] [, SOM_LANDSAT_PATH=value] [, SPHERE_RADIUS=value] [, STANDARD_PARALLEL=value] [, STANDARD_PAR1=value] [, STANDARD_PAR2=value] [, SAT_TILT=value] [, TRUE_SCALE_LATITUDE=value] [, ZONE=value]
The result is a
Set this argument to either a projection index or a scalar string containing the name of the map projection, as described in following tables:
The following are GCTP projections:
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Set this keyword to either an integer code or a scalar string containing the name of the datum to use for the ellipsoid. The default value depends upon the projection selected, but is either the Clarke 1866 ellipsoid (datum 0), or a sphere of radius 6370.997 km (datum 19).
The following datums (or spheroids) are available for use with the DATUM keyword:
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Set this keyword to indicate that the GCTP library should be used for the projection. By default, MAP_PROJ_INIT uses the IDL projection library. This keyword is ignored if the projection exists only in one system (GCTP or IDL), or if the Projection argument is specified as an index.
Set this keyword to a four-element vector of the form
[Latmin, Lonmin, Latmax, Lonmax]
that specifies the boundaries of the region to be mapped. (Lonmin, Latmin) and (Lonmax, Latmax) are the longitudes and latitudes of two points diagonal from each other on the region's boundary.
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Set this keyword to indicate that all parameters that represent angles are specified in radians rather than degrees.
If this keyword is set, any projection parameters which do not apply to the specified projection will be quietly ignored. By default, MAP_PROJ_INIT will issue errors for parameters that do not apply to the specified projection.
The following keywords apply only to some projections. Consult the list under Projection to determine which keywords apply to the projection you have selected.
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Set this keyword to the angle of the central azimuth, in degrees east of North. The default is 0 degrees. The pole is placed at an azimuth of CENTRAL_AZIMUTH degrees counterclockwise of North, as specified by the ROTATION keyword.
Set this keyword to the latitude of the point on the earth's surface to be mapped to the center of the projection plane. Latitude is measured in degrees North of the equator and must be in the range: -90 to +90. The default value is zero.
Set this keyword to the longitude of the point on the earth's surface to be mapped to the center of the map projection. Longitude is measured in degrees east of the Greenwich meridian and must be in the range: -360 to +360. The default value is zero.
Set this keyword to the false easting value (in meters) to be added to each x coordinate for the forward transform, or subtracted from each x coordinate for the inverse transform.
Set this keyword to the false northing value (in meters) to be added to each y coordinate for the forward transform, or subtracted from each y coordinate for the inverse transform.
Set this keyword to the height (in meters) above the earth's surface for satellite projections.
Set this keyword to the longitude in degrees of the central meridian point where the azimuth occurs.
Set this keyword to the azimuth angle, measured in degrees, east of a north-south line that intersects the center line. The center line is defined as the great circle path along which the Mercator cylinder touches the sphere.
Set this keyword to the latitude in degrees of the first point on the center line. The center line is defined as the great circle path along which the Mercator cylinder touches the sphere.
Set this keyword to the latitude in degrees of the second point on the center line. The center line is defined as the great circle path along which the Mercator cylinder touches the sphere.
Set this keyword to the longitude in degrees of the first point on the center line. The center line is defined as the great circle path along which the Mercator cylinder touches the sphere.
Set this keyword to the longitude in degrees of the second point on the center line. The center line is defined as the great circle path along which the Mercator cylinder touches the sphere.
Set this keyword to the number of longitudinal zones to include in the projection.
Set this keyword to a flag indicating what to do with rows with an odd number of columns. The possible values are:
|
Value
|
Description
|
|---|---|
| 0 |
Indicates the extra column is on the right of the projection Y axis.
|
| 1 |
Indicates the extra column is on the left of the projection Y axis.
|
| 2 |
Calculate an even number of columns.
|
Set this keyword to the scale factor at the central meridian (Transverse Mercator projection) or the center of the projection (Hotine Oblique Mercator projection). For the Transverse Mercator projection, the default scale is 0.9996.
Set this keyword to the Oblated Equal Area oval rotation angle in degrees.
Set this keyword to the Oblated Equal Area shape parameter m. The value of OEA_SHAPEM determines the horizontal flatness of the oblong region, and is usually set to a value between one and three.
Set this keyword to the Oblated Equal Area oval shape parameter n. The value of OEA_SHAPEN determines the vertical flatness of the oblong region, and is usually set to a value between one and three.
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Set this keyword to the angle through which the North direction should be rotated around the line between the earth's center and the point (CENTER_LONGITUDE, CENTER_LATITUDE). ROTATION is measured in degrees with the positive direction being clockwise rotation around the line. Values should be in the range -180 to +180. The default value is zero.
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Set this keyword to the length (in meters) of the semimajor axis of the reference ellipsoid. The default is either the Clarke 1866 datum (6378206.4 m) or the Sphere radius (6370997 m), depending upon the projection.
Set this keyword to the length (in meters) of the semiminor axis of the reference ellipsoid. The default is either the Clarke 1866 datum (6356583.8 m) or the Sphere radius (6370997 m), depending upon the projection.
Set this keyword to the orbit inclination angle in degrees of the ascending node, counter-clockwise from equator.
Set this keyword to the longitude in degrees of the ascending orbit at the equator.
Set this keyword to the period in minutes of the satellite revolution.
Set this keyword to the Landsat ratio to compensate for confusion at the northern end of orbit. A typical value is 0.5201613.
Set this keyword to the end of path flag for Landsat, where 0 is the start and 1 is the end.
Set this keyword to the Landsat satellite number.
Set this keyword to the Landsat path number (use 1 for Landsat 1, 2 and 3; use 2 for Landsat 4, 5 and 6).
Set this keyword to the radius (in meters) of the reference sphere. The default is 6370997 m.
Set this keyword to the latitude in degrees of the standard parallel along which the scale is true.
Set this keyword to the latitude in degrees of the first standard parallel along which the scale is true.
Set this keyword to the latitude in degrees of the second standard parallel along which the scale is true.
Set this keyword to the downward tilt in degrees of the camera, in degrees from the projection horizontal.
Set this keyword to the latitude in degrees of true scale.
Set this keyword to an integer giving the zone for the GCTP UTM projection or GCTP State Plane projection.
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See MAP_PROJ_FORWARD for an example of using this function.
Introduced: 5.6
MAP_PROJ_FORWARD, MAP_PROJ_INVERSE, MAP_SET